Method for purifying an aliphatic polyester

ABSTRACT

The present invention relates to a continuous process for purifying a chain-extended aliphatic polyester constructed from aliphatic dicarboxylic acids and aliphatic diols in a degassing apparatus, wherein the crude polyester is degassed for 3 to 30 minutes at a pressure of 0.01 to 5 mbar in the presence of 1% to 7% by weight, based on the total weight of the crude polyester, of an entraining agent.

The present invention relates to a continuous process for purifying achain-extended aliphatic polyester constructed from aliphaticdicarboxylic acids and aliphatic diols in a degassing apparatus, whereinthe crude polyester is degassed with an average residence time of 3 to30 minutes and at a pressure of 0.01 to 5 mbar in the presence of 1% to7% by weight, based on the total weight of the crude polyester, of anentraining agent.

Processes for continuously producing aliphatic polyesters such aspolybutylene succinate (PBS), polybutylene succinate-co-adipate (PBSA)or polybutylene succinate-co-sebacate (PBSSe) are known from theliterature (see WO-A 2009/127556 and EP-A 2228399). These documentsdescribe the depletion of tetrahydrofuran formed and EP-A 2228399 alsodescribes the depletion of cyclic dimers. However, the processesdescribed in these documents do not result in sufficient depletion ofthe cyclic byproducts to obtain for example approval for contact withfoodstuffs according to EU 10/2011.

EP-A 2623540 describes a process for purifying aliphatic polyesters suchas polybutylene succinate (PBS), polybutylene succinate-co-adipate(PBSA) or polybutylene succinate-co-sebacate (PBSSe), in which cyclicbyproducts are extracted by means of extraction with solvents. Thedisadvantage of this extraction process is that impurities trapped inthe granulate cannot be depleted and contamination of the polyester withsolvents can result. This process is altogether rather complex andcostly.

The present invention accordingly has for its object to find anefficient and scaleable continuous process for purifying aliphaticpolyesters which does not have the above-described disadvantages.

The inventors have surprisingly found a continuous process for purifyinga chain-extended aliphatic polyester constructed from aliphaticdicarboxylic acids and aliphatic diols in a degassing apparatus, whereinthe crude polyester is degassed in the degassing apparatus for 3 to 30minutes at a pressure of 0.01 to 5 mbar in the presence of 1% to 7% byweight, based on the total weight of the crude polyester, of anentraining agent.

The invention is more particularly described hereinbelow.

Aliphatic polyesters are for example produced—as described in WO-A2009/127556 and EP-A 2228399—in a manner comprising the steps of a)esterification, b) polycondensation and c) chain extension.

In a preliminary step a mixture of the aliphatic dihydroxyl compounds,the aliphatic dicarboxylic acids and optionally further comonomers,preferably without the addition of the catalyst, is mixed to afford apaste or slurry and preferably brought to a temperature of 20° C. to 90°C. or alternatively the liquid mixture of esters of the dicarboxylicacids and dihydroxyl compound and optionally further comonomers,preferably without addition of a catalyst, is continually introducedinto a reactor for esterification (pre-condensation) and

-   -   a) continuously esterified/transesterified with the total amount        or a sub-amount of the catalyst and pre-condensed up to a        viscosity number according to DIN 53728 of preferably 20 to 70        cm³/g;    -   b) the product obtainable from a) is polycondensed in a        polycondenser up to a viscosity number according to DIN 53728 of        preferably 60 to 170 cm³/g;    -   c) in a further step is continuously reacted with a chain        extender C up to a viscosity number according to DIN 53728 of        preferably 150 to 320 cm³/g; and    -   d) the crude polyester obtainable from c) is degassed in a        degassing apparatus suitable therefor at a pressure of 0.01 to 5        mbar in the presence of 1% to 7% by weight based on the total        weight of the crude polyester of an entraining agent.

Aliphatic polyesters are to be understood as meaning polyestersconstructed predominantly from monomeric aliphatic dicarboxylic acidsand aliphatic diols.

Contemplated aliphatic dicarboxylic acids or ester-forming derivativesthereof in general include those having 2 to 40 carbon atoms, preferably4 to 14 carbon atoms. They may preferably be linear or branched. Thecycloaliphatic dicarboxylic acids usable in the context of the presentinvention are generally those having 7 to 10 carbon atoms and inparticular those having 8 carbon atoms. However, it is also possible inprinciple to employ dicarboxylic acids having a greater number of carbonatoms, for example having up to 30 carbon atoms.

Examples include: malonic acid, succinic acid, glutaric acid,2-methylglutaric acid, 3-methylglutaric acid, adipic acid, pimelic acid,suberic acid, azelaic acid, sebacic acid, undecanedioic acid,dodecanedioic acid, brassylic acid, tetradecanedioic acid, fumaric acid,2,2-dimethylglutaric acid, suberic acid, dimer fatty acid (for exampleEmpol® 1061 from BASF), 1,3-cyclopentanedicarboxylic acid,1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid,diglycolic acid, itaconic acid, maleic acid, maleic anhydride and2,5-norbornanedicarboxylic acid.

Likewise employable ester-forming derivatives of the abovementionedaliphatic or cycloaliphatic dicarboxylic acids include in particulardi-C₁- to C₆-alkyl esters, such as dimethyl, diethyl, di-n-propyl,diisopropyl, di-n-butyl, diisobutyl, di-t-butyl, di-n-pentyl,diisopentyl or di-n-hexyl esters. Anhydrides of the dicarboxylic acidsmay likewise be employed.

These dicarboxylic acids or the ester-forming derivatives thereof may beused individually or as a mixture of two or more thereof.

It is preferable to employ succinic acid, adipic acid, azelaic acid,sebacic acid, brassylic acid or their respective ester-formingderivatives or mixtures thereof. It is particularly preferable to employsuccinic acid, adipic acid or sebacic acid or their respectiveester-forming derivatives or mixtures thereof. It is particularlypreferable to employ succinic acid or mixtures of succinic acid withpreferably up to 25 mol % of adipic acid or preferably up to 10 mol % ofsebacic acid or their ester-forming derivatives, such as their alkylesters.

Succinic acid, azelaic acid, sebacic acid and brassylic acidadditionally have the advantage that they are obtainable as renewableraw materials.

Aliphatic diols are generally to be understood as meaning branched orpreferably linear alkanediols having 2 to 12 carbon atoms, preferably 3to 6 carbon atoms.

Examples of suitable alkanediols are ethylene glycol, 1,2-propanediol,1,3-propanediol, 1,2-butanediol, 1,4-butanediol, 1,5-pentanediol,1,6-hexanediol 2,4-dimethyl-2-ethylhexane-1,3-diol,2,2-dimethyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol,2-ethyl-2-isobutyl-1,3-propanediol, 2,2,4-trimethyl-1,6-hexanediol,especially ethylene glycol, 1,3-propanediol, 1,4-butanediol and2,2-dimethyl-1,3-propanediol (neopentyl glycol); cyclopentanediol,1,4-cyclohexanediol, 1,2-cyclohexanedimethanol,1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol or2,2,4,4-tetramethyl-1,3-cyclobutanediol. 1,4-butanediol are particularlypreferred. Mixtures of different alkanediols may also be employed.

In the process steps: preliminary step and esterification a) a ratio ofdiol to dicarboxylic acid of generally 1.0 to 2.5 and preferably 1.2 to2.2 is established.

The aliphatic polyesters may further comprise a branching agentcomprising at least three functional groups. Particularly preferredbranching agents have three to six hydroxyl groups or carboxylic acidgroups. Examples include: tartaric acid, citric acid, malic acid;trimethylolpropane, trimethylolethane; pentaerythritol; polyethertriolsand glycerol, trimesic acid, trimellitic acid, trimellitic anhydride,pyromellitic acid and pyromellitic dianhydride. Preference is given topolyols such as trimethylolpropane, pentaerythritol and especiallyglycerol. The branching agents make it possible to constructbiodegradable polyesters having a structural viscosity. The rheologicalbehavior of the melts improves; the polyesters are easier to process,for example are more readily drawable into films by melt solidification.The branching agents have a shear-thinning effect, i.e. viscosity underload decreases.

The branching agents are preferably employed in amounts of 0.01% to 2%by weight, preferably 0.05% to 1% by weight, particularly preferably0.08% to 0.20% by weight, based on the polymer amount after step a).

In addition to the dicarboxylic acids and diols the aliphatic polyestersmay comprise further of the following components selected from the groupconsisting of: dihydroxyl compound and hydroxycarboxylic acid.

Suitable dihydroxyl compounds include diethylene glycol, triethyleneglycol, polyethylene glycol, polypropylene glycol andpolytetrahydrofuran (poly-THF), particularly preferably diethyleneglycol, triethylene glycol and polyethylene glycol, it also beingpossible to employ mixtures thereof or compounds having differingvariables n (see formula I), for example polyethylene glycol comprisingpropylene units (n=3), for example obtainable by polymerizationaccording to methods known per se initially of ethylene oxide andsubsequently with propylene oxide, particularly preferably a polymerbased on polyethylene glycol having differing variables n, wherein unitsformed from ethylene oxide predominate. The molecular weight (M_(n)) ofthe polyethylene glycol is generally in the range from 250 to 8000,preferably from 600 to 3000 g/mol.

In one of the preferred embodiments it is possible to employ for example15 to 98 mol %, preferably 70 to 99.5 mol %, of a diol and 0.2 to 85 mol%, preferably 0.5 to 30 mol %, of the dihydroxyl compounds recitedhereinabove for production of the polyesters.

Production of polyesters may employ a hydroxycarboxylic acid such as:glycolic acid, D-lactic acid, L-lactic acid, D,L-lactic acid,6-hydroxyhexanoic acid, cyclic derivatives thereof such as glycolide(1,4-dioxane-2,5-dione), D- or L-dilactide(3,6-dimethyl-1,4-dioxane-2,5-dione), p-hydroxybenzoic acid and alsotheir oligomers and polymers such as 3-polyhydroxybutyric acid,polyhydroxyvaleric acid, polylactide (obtainable for example as Ingeo®(NatureWorks)), the low molecular weight and cyclic derivatives thereofbeing particularly preferable for production of aliphatic polyesters.

The hydroxycarboxylic acids may be employed for example in amounts from0.01% to 50% by weight, preferably from 0.1% to 15% by weight, based onthe amount of the monomers.

The use of chain extenders C is typically effected at the end of thepolycondensation in a separate step c).

Employable as component C1 are an isocyanate or a mixture of differentisocyanates. Aromatic or aliphatic diisocyanates may be employed.However, it is also possible to employ higher-functional isocyanates.

In the context of the present invention an aromatic diisocyanate C1 isto be understood as meaning especially tolylene 2,4-diisocyanate,tolylene 2,6-diisocyanate, 2,2′-diphenylmethane diisocyanate,2,4′-diphenylmethane diisocyanate, 4,4′-diphenylmethane diisocyanate,naphthylene 1,5-diisocyanate or xylylene diisocyanate.

Particularly preferred as component C1 among these are 2,2′-, 2,4′- and4,4′-diphenylmethane diisocyanate. The latter diisocyanates aregenerally employed as mixtures.

Also contemplated as tricyclic isocyanate C1 istri(4-isocyanatophenyl)methane. The polycyclic aromatic diisocyanatesare generated for example in the production of mono-cyclic or bicyclicdiisocyanates.

The component C may also comprise urethione groups in subordinateamounts, for example up to 5% by weight, based on the total weight ofthe component C, for example for capping the isocyanate groups.

In the context of the present invention an aliphatic diisocyanate C1 isto be understood as meaning especially linear or branched alkylenediisocyanates or cycloalkylene diisocyanates having 2 to 20 carbonatoms, preferably 3 to 12 carbon atoms, for example 1,6-hexamethylenediisocyanate, isophorone diisocyanate ormethylenebis(4-isocyanatocyclohexane). Particularly preferred aliphaticdiisocyanates C are isophorone diisocyanate and in particular1,6-hexamethylene diisocyanate.

Preferred isocyanurates C1 include the aliphatic isocyanurates derivingfrom alkylene diisocyanates or cycloalkylene diisocyanates having 2 to20 carbon atoms, preferably 3 to 12 carbon atoms, for example isophoronediisocyanate or methylenebis(4-isocyanatocyclohexane). The alkylenediisocyanates may be either linear or branched. Particular preference isgiven to isocyanurates based on n-hexamethylenediisocyanate, for examplecyclic trimers, pentamers or higher oligomers of 1,6-hexamethylenediisocyanate.

The component 01 may generally be employed in amounts of 0.01% to 4% byweight, preferably 0.05% to 2% by weight, particularly preferably 0.2%to 1.2% by weight, based on the polymer amount after step b).

Suitable di- or oligofunctional peroxides (component C2) include forexample the following compounds: benzoyl peroxide,1,1-bis(t.-butylperoxy)-3,3,5-trimethylcyclohexane,1,1-bis(t.-butylperoxy)methylcyclododecane,n-butyl-4,4-bis(butylperoxy)valerate, di-cumyl peroxide, t.-butylperoxybenzoate, dibutyl peroxide,α,α-bis(t.-butylperoxy)diisopropylbenzene,2,5-dimethyl-2,5-di(t.-butylperoxy)hexane,2,5-dimethyl-2,5-di(t.-butylperoxy)hex-3-yne and t.-butyl peroxycumene.

The component C2 is employed at 0.01% to 4% by weight, preferably at0.1% to 2% by weight and particularly preferably at 0.2% to 1% by weightbased on the polyester.

Suitable as component C3 are difunctional or oligofunctional epoxidessuch as: hydro-quinone, diglycidyl ethers, resorcinol diglycidyl ethers,1,6-hexanediol diglycidyl ether and hydrogenated bisphenol A diglycidylether. Other examples of epoxides comprise diglycidyl terephthalate,diglycidyl tetrahydrophthalate, diglycidyl hexahydrophthalate,dimethyldiglycidyl phthalate, phenylene diglycidyl ether, ethylenediglycidyl ether, tri-methylene diglycidyl ether, tetramethylenediglycidyl ether, hexamethylene diglycidyl ether, sorbitol diglycidylether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidylether, diglycerol polyglycidyl ether, glycerol polyglycidyl ether,trimethylolpropane polyglycidyl ether, resorcinol diglycidyl ether,neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether,diethylene glycol diglycidyl ether, polyethylene glycol diglycidylether, propylene glycol diglycidyl ether, dipropylene glycol diglycidylether, polypropylene glycol diglycidyl ether, and polybutylene glycoldiglycidyl ether.

Especially suitable as component C3a is an epoxy-containing copolymerbased on styrene, acrylic ester and/or methacrylic ester d3a. Theepoxy-bearing units are preferably glycidyl (meth)acrylates. Copolymershaving a glycidyl methacrylate proportion of greater than 20%,particularly preferably of greater than 30% and especially preferably ofgreater than 50% by weight of the copolymer have proven advantageous.The epoxy equivalent weight (EEW) in these polymers is preferably 150 to3000 and especially preferably 200 to 500 g/equivalent. The averagemolecular weight (weight-average) Mw of the polymers is preferably 2000to 25 000, in particular 3000 to 8000. The average molecular weight(number-average) M_(n) of the polymers is preferably 400 to 6000, inparticular 1000 to 4000. The polydispersity (Q) is generally between 1.5and 5. Epoxy-containing copolymers of the abovementioned type are forexample marketed by BASF Resins B.V. under the Joncryl® ADR brand. Aparticularly suitable chain extender is Joncryl® ADR 4368.

The component C3 is employed at 0.01% to 4% by weight, preferably at0.1% to 2% by weight and particularly preferably at 0.2% to 1% by weightbased on the polyester.

Contemplated as component C4 are di- or oligo-functional oxazolines,oxazines, caprolactams and/or carbodiimides.

Bisoxazolines are generally obtainable by the process from Angew. Chem.Int. Ed., vol. 11 (1972), pages 287-288. Particularly preferredbisoxazolines and bisoxazines are those in which the bridging memberrepresents a single bond, a (CH₂)_(z)-alkylene group where z=2, 3 or 4such as methylene, ethane-1,2-diyl, propane-1,3-diyl, propane-1,2-diyl,or a phenylene group. Particularly preferred bisoxazolines include2,2′-bis(2-oxazoline), bis(2-oxazolinyl)methane,1,2-bis(2-oxazolinyl)ethane, 1,3-bis(2-oxazolinyl)propane or1,4-bis(2-oxazolinyl)butane, in particular 1,4-bis(2-oxazolinyl)benzene,1,2-bis(2-oxazolinyl)benzene or 1,3-bis(2-oxazolinyl)benzene. Furtherexamples are: 2,2′-bis(2-oxazoline), 2,2′bis(4-methyl-2-oxazoline),2,2′-bis(4,4′-dimethyl-2-oxazoline), 2,2′-bis(4-ethyl-2-oxazoline),2,2′-bis(4,4′-diethyl-2-oxazoline), 2,2′-bis(4-propyl-2-oxazoline),2,2′-bis(4-butyl-2-oxazoline), 2,2′-bis(4-hexyl-2-oxazoline),2,2′-bis(4-phenyl-2-oxazoline), 2,2′-bis(4-cyclohexyl-2-oxazoline),2,2′-bis(4-benzyl-2-oxazoline),2,2′-p-phenylenebis(4-methyl-2-oxazoline),2,2′-p-phenylenebis(4,4′dimethyl-2-oxazoline),2,2′-m-phenylenebis(4-methyl-2-oxazoline),2,2′-m-phenylenebis(4,4′-dimethyl-2-oxazoline),2,2′-hexamethylenebis(2-oxazoline), 2,2′-octamethylenebis(2-oxazoline),2,2′-decamethylenebis(2-oxazoline),2,2′-ethylenebis(4-methyl-2-oxazoline),2,2′-tetramethylenebis(4,4′-dimethyl-2-oxazoline),2,2′-9,9′-diphenoxyethanebis(2-oxazoline),2,2′-cyclohexylenebis(2-oxazoline), and2,2′-diphenylenebis(2-oxazoline).

Preferred bisoxazines are 2,2′-bis(2-oxazine), bis(2-oxazinyl)methane,1,2-bis(2-oxazinyl)ethane, 1,3-bis(2-oxazinyl)propane, or1,4-bis(2-oxazinyl)butane, in particular 1,4-bis(2-oxazinyl)benzene,1,2-bis(2-oxazinyl)benzene, or 1,3-bis(2-oxazinyl)benzene.

Carbodiimides and polymeric carbodiimides are marketed by Lanxess underthe brand name Stabaxol® for example.

Examples are: N,N′-di-2,6-diisopropylphenylcarbodiimide,N,N′-di-o-tolylcarbodiimide, N,N′-diphenylcarbodiimide,N,N′-dioctyldecylcarbodiimide, N,N′-di-2,6-dimethylphenylcarbodiimide,N-tolyl-N′-cyclohexylcarbodiimide,N,N′-di-2,6-di-tert-butylphenylcarbodiimide,N-tolyl-N′-phenylcarbodiimide, N,N′-di-p-nitrophenylcarbodiimide,N,N′-di-p-aminophenylcarbodiimide, N,N′-di-p-hydroxyphenylcarbodiimide,N,N′-dicyclohexylcarbodiimide, N,N′-di-p-tolylcarbodiimide,p-phenylenebisdi-o-tolylcarbodiimide,p-phenylenebisdicyclohexylcarbodiimide,hexa-methylenebisdicyclohexylcarbodiimide,4,4′-dicyclohexylmethanecarbodiimide, ethylenebisdiphenylcarbodiimide,N,N′-benzylcarbodiimide, N-octadecyl-N′-phenylcarbodiimide,N-benzyl-N′-phenylcarbodiimide, N-octadecyl-N′-tolylcarbodiimide,N-cyclohexyl-N′-tolylcarbodiimide, N-phenyl-N′-tolylcarbodiimide,N-benzyl-N′-tolylcarbodiimide, N,N′-di-o-ethylphenylcarbodiimide,N,N′-di-p-ethylphenylcarbodiimide,N,N′-di-o-isopropylphenylcarbodiimide,N,N′-di-p-isopropylphenylcarbodiimide,N,N′-di-o-isobutylphenylcarbodiimide,N,N′-di-p-isobutylphenylcarbodiimide,N,N′-di-2,6-diethylphenylcarbodiimide,N,N′-di-2-ethyl-6-isopropylphenylcarbodiimide,N,N′-di-2-isobutyl-6-isopropylphenylcarbodiimide,N,N′-di-2,4,6-trimethylphenylcarbodiimide,N,N′-di-2,4,6-triisopropylphenylcarbodiimide,N,N′-di-2,4,6-triisobutylphenylcarbodiimide, diisopropylcarbodiimide,dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcar-bodiimide,tert-butylisopropylcarbodiimide, di-β-naphthylcarbodiimide anddi-tert-butylcarbodiimide.

The component C4 is employed at 0.01% to 4% by weight, preferably at0.1% to 2% by weight and particularly preferably at 0.2% to 1% by weightbased on the polyester.

Preference is given to aliphatic polyesters i comprising the followingcomponents:

-   i-a) 90 to 100 mol % based on the components i-a to i-b of succinic    acid;-   i-b) 0 to 10 mol % based on the components i-a to i-b of one or more    C₆-C₂₀ dicarboxylic acids and especially preferably adipic acid,    azelaic acid, sebacic acid or brassylic acid;-   i-c) 99 to 100 mol % based on the components i-a to i-b of    1,3-propanediol or especially preferably 1,4-butanediol;-   i-d) 0.1% to 1% by weight based on the components i-a to i-c of a    chain extender C and/or branching agent.

The process according to the invention is especially suitable forproducing the aliphatic polyesters: polybutylene adipate (PBA),polybutylene succinate adipate (PBSA), polybutylene succinate sebacate(PBSSe), polybutylene sebacate (PBSe) and particularly preferablypolybutylene succinate (PBS). Aliphatic polyesters are marketed, forexample, by Showa Highpolymers under the name Bionolle and by Mitsubishiunder the name GS Pla.

The aliphatic polyesters produced with the process according to theinvention generally have viscosity numbers according to DIN 53728 of 150to 320 cm³/g and preferably 150 to 250 cm³/g.

The MVR (melt volume rate) according to EN ISO 1133 (190° C., 2.16 kgweight) is generally 0.1 to 150 cm³/10 min, preferably 10 to 150 cm³/10min.

The acid numbers according to DIN EN 12634 are generally 0.01 to 1.2 mgKOH/g, preferably 0.1 to 1.0 mg KOH/g and especially preferably 0.1 to0.7 mg KOH/g.

The recited aliphatic and semiaromatic polyesters and the polyestermixtures according to the invention are biodegradable.

In the context of the present invention the feature “biodegradable” isfulfilled for a substance or a substance mixture when this substance orthe substance mixture has a percentage degree of biodegradationaccording to DIN EN 13432 of at least 90%.

Biodegradability generally results in the polyester (mixtures)decomposing in an appropriate and verifiable timeframe. The degradationmay be effected enzymatically, hydrolytically, oxidatively and/or by theaction of electromagnetic radiation, for example UV radiation, and mayusually be brought about predominantly by the action of microorganismssuch as bacteria, yeasts, fungi and algae. Biodegradability may bequantified for example when polyesters are mixed with compost and storedfor a certain time. For example according to DIN EN 13432 002-free airis passed through matured compost during composting and said compost issubjected to a defined temperature program. Biodegradability is heredefined via the ratio of the net CO₂ release from the sample (aftersubtracting the CO₂ release by the compost without a sample) to themaximum CO₂ release from the sample (calculated from the carbon contentof the sample) as a percentage degree of biodegradation. Biodegradablepolyester (mixtures) generally show distinct signs of degradation suchas fungus growth and tear and hole formation even after just a few daysof composting.

Other methods for determining biodegradability are described for examplein ASTM D 5338 and ASTM D 6400.

EU Regulation 10/2011 specifies threshold values for plastics materialsthat are in contact with food products. Packaging materials made ofnon-purified aliphatic polyesters such as polybutylene succinate (PBS)do not meet the requirements of this standard and are thereforeunsuitable for foodstuffs applications. Especially the cyclic impuritiesin the polyester such as THF, cyclic monomers, dimers, trimers andtetramers can migrate out of the packaging material under the varioustest conditions. The process according to the invention now providesaliphatic polyesters which are distinctly depleted in cyclic impuritiesand which achieve the threshold values required in EU Regulation10/2011. The process according to the invention has also proven moreefficient than the processes described in EP-A 228399 and EP-A 2623540.

The process according to the invention is more particularly describedhereinbelow:

The chain-extended aliphatic polyesters are produced as described in theliterature or in the introduction.

In the chain extension the polycondensed polyester is introduced into anextruder, a continuous kneader (List reactor) or a static mixer togetherwith 0.01% to 4% by weight, preferably 0.1% to 2% by weight andespecially preferably 0.5% to 1.2% by weight based on the polyester of achain extender. Internals that may be employed include: in the case of astatic mixer SMR, SMX, or SMXL elements or combinations thereof, forexample from Sulzer Chemtech AG, Switzerland. Examples of a List reactorinclude depending on the field of application a single-screw DISCOTHERMB reactor or twin-screw CRP and ORP reactors. Suitable extruders includesingle-screw or twin-screw extruders.

Suitable chain extenders include the above-described isocyanates orisocyanurates C1, peroxides C2 and epoxides C3a. These diisocyanates areselected for example from the group consisting of tolylene2,4-diisocyanate, tolylene 2,6-diisocyanate, 4,4′- and2,4′-diphenylmethane diisocyanate, naphthylene 1,5-diisocyanate,xylylene diisocyanate, hexamethylene diisocyanate, isophoronediisocyanate and methylenebis(4-isocyanatocyclohexane). Hexamethylenediisocyanate is particularly preferred.

The chain extension reaction is carried out at reaction temperatures of220° C. to 270° C., preferably 230° C. to 250° C., and atsuperatmospheric pressure or atmospheric pressure depending on thesystem used. Residence times of 2 to 30 minutes, preferably 4 to 15minutes, allow production of aliphatic/aromatic polyesters having aviscosity number according to DIN 53728 of 160 to 250 cm³/g and acidnumbers according to DIN EN 12634 of preferably 0.5 to 1.2 mg KOH/g andespecially preferably of 0.6 to 1.0 mg KOH/g.

The MVR (melt volume rate) according to EN ISO 1133 (190° C., 2.16 kgweight) after step c is generally 0.5 to 6.0 cm³/10 min, preferably 1.0to 5.0 cm³/10 min and particularly preferably 1.5 to 3 cm³/10 min.

The reactor in which the chain reaction is performed has theabove-described internals which ensure thorough commixing of the productstream.

Due to the marked viscosity increase during the chain extension reactionit may be advantageous to run the chain extension reaction in thereactor only until the chain extender has fully reacted at least withone functional unit. Chain formation may be completed for example in aseparate stirred tank or in a tube without internals. This makes itpossible to avoid blockages and wall deposits.

The fully reacted melt is generally transferred directly to thedegassing apparatus.

The purification according to the invention of the chain-extendedaliphatic polyester constructed from aliphatic dicarboxylic acids andaliphatic diols is carried out in a degassing apparatus, wherein thecrude polyester resides in the degassing apparatus for 3 to 30 minutesat a pressure of 0.01 to 5 mbar in the presence of 1% to 7% by weight,based on the total weight of the crude polyester, of an entrainingagent.

In a preferred embodiment of the process according to the invention, athin film evaporator is selected as degassing apparatus. The thin filmevaporator has the following general characteristics: The evaporatorsurface is a tube having a mechanical stirring means in the middle. Themelt is passed on to the vertical evaporator surface from above. Thethin film evaporator generates a thin film (melt film) on the inner wallof a heated outer shell by mechanical means using a rotor. This resultsin continuous surface replacement, thus ensuring good mass transfer andtherefore a high degassing performance. The degassing performance isachieved by addition of a stripping agent (for example water or steam)which is supplied in countercurrent. Also required for good degassingperformance is a vacuum of not more than 5 mbar.

The shape and configuration of the individual rotor blades allowstransport of the viscous product to the discharge section of theprocessor. The film thickness and the melt conveying is likewisedependent on the geometry of the rotor blades. The large free gas volumeallows a high evaporative concentration ratio in one stage without therisk of product entrainment into the condensation system.

The following conditions apply to the degassing apparatus: the averageresidence times in the degassing apparatus are 3 to 30 minutes—longerresidence times would lead to increased degradation of the polycondensedpolyester, with shorter residence times, the depletion of the cyclicoligomers is not satisfactory enough.

It may also be advantageous to reduce the activity of the reactioncatalyst by addition of one-off or further amounts of theabove-described deactivators such as for example phosphorous acid.

The temperatures employed in the degassing apparatus are generally 180°C. to 260° C. and preferably 200° C. to 240° C.

The entraining agent is preferably introduced into the gas space of thedegassing apparatus. This has the advantage that a homogeneous polyesterfilm is formed in the degassing apparatus and for example blisterformation or foaming in the polyester film are avoided.

Suitable entraining agents are, as described above, water, ethanol,nitrogen, carbon dioxide, acetone and cyclic polypropylene carbonate.Water which is introduced into the gas space of the degassing apparatusas steam is particularly suitable.

The amount of the entraining agent is generally between 1% and 7% byweight, preferably 2% to 5% by weight, based on the polyester at the endof step b). Greater amounts of entraining agent result in anunacceptable impairment of the vacuum established in the degassingapparatus. At a lower entraining agent concentration the crude polyesteris insufficiently depleted in cyclic impurities such as THF and cyclicmonomers, dimers, trimers and tetramers of the polyester.

In the degassing apparatus the polymer melt generally forms an averagefilm thickness of less than 5 mm, preferably less than 2 mm andespecially preferably less than 1 mm.

Suitable degassing apparatuses, in addition to the preferred thin filmevaporator, include a spinning-disc reactor, cage reactor, falling filmevaporator or planetary roll extruder. WO 2014/195176 describes aprocess for drastically reducing the emissions of TOC (total organiccarbon—such as for example THF) for aromatic or aliphatic-aromaticpolyesters. The inventors have found that this is likewise possible foraliphatic polyesters such as PBS when before introduction into adegassing apparatus B′ the crude polyester is introduced with 0.01% to2% by weight of the acrylic acid polymer described in WO 2014/195176 andconstructed from constructed from a) 70% to 100% by weight of acrylicacid and b) 0% to 30% by weight of at least one other ethylenicallyunsaturated monomer copolymerizable with acrylic acid and selected fromthe group of monoethylenically unsaturated carboxylic acids.

The aliphatic polyesters obtainable by the process according to theinvention such as for example PBS are suitable for numerous applicationssuch as injection molded products, thermoforming products, films orfoams. The aliphatic polyesters are often employed in mixtures withfurther biopolymers such as polylactic acid, polyhydroxyalkanoates,biodegradable aliphatic-aromatic polyesters, starch, mineral fillers orother additives such as for example lubricants, nucleating agents,plasticizers or pigments.

The process according to the invention makes it possible to achieve adistinct depletion of cyclic impurities. In the case of1,4-butanediol-containing polyesters the residual THF content of thealiphatic polyester may generally be reduced to half or preferably aquarter and especially preferably a tenth of the original THF content.The purified aliphatic polyester generally has a residual THF content ofless than 50 ppm, preferably less than 30 ppm and especially preferablyless than 10 ppm.

The cyclic oligomers content of the aliphatic polyester can also bedistinctly reduced. In the case of PBS for example the process accordingto the invention generally reduces the content of cyclic monomer andcyclic dimer by more than 30%, preferably more than 40% and inparticular more than 50%. In a component part produced from thealiphatic polyester such as a film precisely these two cyclic oligomersundergo more severe migration than the correspondingly higher oligomers.The disruptive cyclic monomers and dimers in PBS may generally bereduced to less than 0.8% by weight, preferably less than 0.7% by weightand especially preferably less than 0.6% by weight of the polyester. Theefficient depletion of the cyclic monomers and dimers in the processaccording to the invention makes it possible to obtain approval forcontact with foodstuffs according to EU 10/2011.

To produce these polyester mixtures or polyester formulations it hasproven advantageous when after the degassing apparatus thechain-extended aliphatic polyester depleted of cyclic impurities iscontinuously sent for compounding with further polymers and auxiliarieswithout intermediate isolation such as for example underwatergranulation. In addition to the cost-saving achieved by omitting thegranulation step the aliphatic polyester need not be melted. Renewedformation of cyclic impurities that might result from thermal stress cantherefore be avoided.

The process according to the invention makes it possible to scalably andefficiently produce chain-extended aliphatic polyesters which are alsopoor in cyclic impurities.

Methods of Measurement:

Viscosity numbers were determined according to DIN 53728 Part 3, Jan. 3,1985. The solvent mixture: phenol/dichlorobenzene in a 50/50 weightratio was employed.

The melt of volume rate (MVR) was determined according to ISO 1133. Testconditions of 190° C., 2.16 kg were used. The melting time was 4minutes. The MVR describes the rate of extrusion of a molten plasticsmolding composition through an extrusion die of defined length anddefined diameter under the above-described conditions: temperature,loading and piston position. The volume extruded in a defined time inthe barrel of an extrusion plastometer is determined.

Performance Testing:

The molecular weights Mn and Mw of the semiaromatic polyesters weredetermined by SEC according to DIN 55672-1. Eluent:hexafluoroisopropanol (HFIP)+0.05% by weight potassium trifluoroacetate;calibration performed with narrow-distribution polymethyl methacrylatestandards. Evaluation had to be aborted after 18.83 mL (about M=300g/mol) since the chromatogram is disrupted by impurities in thesample/in the SEC eluent for smaller molar masses.

Melt volume rate MVR at 190° C. and 2.16 kg according to ISO 1133-1 DE

The oligomers were characterized by gas chromatography coupled with massspectroscopy (GC-MS). 24.41 mg of sample were dissolved in 1.2 ml ofdichloromethane. The ampoule was placed on a tube roller for 30 minutes.Ionization was by positive ion, chemical ionization and electron impactionization. Individual resolution is employed.

Starting Materials

1,4-Butanediol from BASF SE, succinic acid from DMS N.V. and titaniumorthotitanate from Sigma Aldrich.

Polyester i:

i-1 Polybutylene Succinate:

82.0 g of 1,4-butanediol, 82.7 g of succinic acid, 0.09 g of glyceroland 0.13 g of titanium orthotitanate were initially charged and meltedat 120° C. The temperature was then increased to 160° C. and water wasdistilled off. A vacuum was then applied, the temperature was increasedto 250° C. and polycondensation was carried out up to the desiredviscosity number. The temperature was then reduced to 220° C. and thepolymer was finished by addition of 1.2 g of hexamethylene diisocyanate.The oligomer proportion after GPC was 1.34% by weight.

Performing the Degassing in the Melt

The polyester granulate was continuously melted with the aid of akneader, the melting temperature at the outlet of the kneader beingabout 200° C.-220° C. The necessary melting energy was supplied to thematerial via the heater bands of the cylinder and via shearing(rotational speed of the kneader). Alternatively, it was also possiblefor the polyester to be melted using a single-screw or twin-screwextruder in order to be then supplied from above (laterally) to thevertical thin film evaporator via a heated pipe using a melt pump. Inthe experiments, the throughput was between 15 and 40 kg/h.

In the thin film evaporator (Filmtruder), the melt was drawn out to forma thin film having a thickness of about 1 mm with the aid of a rotor andthe appropriate blade geometries and transported downward. The outershell of the evaporator was heated (200-280° C.) and the residence timein the thin film evaporator was determined/varied via the rotor speed.

At the same time, it was possible to supply an entraining agent frombelow in countercurrent and, for better degassing, a vacuum was applied.Once the melt had arrived in the lower part of the thin film evaporator,it was continuously discharged with the aid of a melt pump and drawn outto form strands via a die plate. These were cooled in a water bath andsupplied to a granulator in order to then obtain granulate again. As analternative to strand granulation, it was also possible to useunderwater granulation after the melt discharge pump.

The oligomers were removed under vacuum in the upper region of the thinfilm evaporator and subsequently condensed.

1.-11. (canceled)
 12. A continuous process for purifying achain-extended aliphatic polyester constructed from aliphaticdicarboxylic acids and aliphatic diols in a degassing apparatus,comprising degassing a crude polyester with an average residence time of3 to 30 minutes and at a pressure of 0.01 to 5 mbar in the presence of1% to 7% by weight, based on the total weight of the crude polyester, ofan entraining agent.
 13. The process according to claim 12, wherein theentraining agent is introduced into the gas space of the degassingapparatus.
 14. The process according to claim 12, wherein the entrainingagent is selected from the group consisting of additionally introducedwater, ethanol, nitrogen, carbon dioxide, acetone, and cyclic propylenecarbonate.
 15. The process according to claim 12, wherein the degassingapparatus is a thin film evaporator.
 16. The process according to claim12, wherein the degassing apparatus has an internal temperature of 180°C. to 260° C. and preferably 200° C. to 240° C.
 17. The processaccording to claim 12, wherein the crude polyester in the degassingapparatus has a film thickness of less than 2 mm and preferably lessthan 1 mm.
 18. The process according to claim 12, wherein the aliphaticpolyester comprises the aliphatic diol 1,4-butanediol.
 19. The processaccording to claim 12, wherein the aliphatic polyester is a polybutylenesuccinate.
 20. The process according to claim 12, wherein the crudepolyester has an MVR according to DIN EN 1133-1 of 01.03.2012 (190° C.,2.16 kg) of 0.5 to 50 cm³/10 min.
 21. The process according to claim 18,wherein before introduction into the degassing apparatus the crudepolyester is mixed with 0.01% to 2% by weight of an acrylic acid polymerconstructed from: a) 70% to 100% by weight of acrylic acid and b) 0% to30% by weight of at least one other ethylenically unsaturated monomercopolymerizable with acrylic acid and selected from the group ofmonoethylenically unsaturated carboxylic acids.
 22. The processaccording to claim 12, wherein the polyester purified from the degassingapparatus is sent for compounding with further polymers and auxiliarieswithout a granulation step.